1. Field of the Invention
The present invention relates to an emergency shutdown monitoring module that communicates in series or parallel with the central processing unit of a programmable controller.
2. Discussion of the Background
Production shops and the technical installations of premises are subject to increasingly strict safety requirements.
In order to activate a switch controlling the power supply of a machine by means of a protection apparatus (emergency shutdown), a safety module is used that will ensure a reliable relay and eliminate the risks of faults in the control circuit (inputs), the power circuit (outputs) or in internal components of the safety module.
When this type of safety module is used with a programmable logic controller, the safety module remains independent of the programmable controller.
The present invention aims to provide a monitoring module for programmable controllers equipped with a hardwired logic safety function. The status of the external sensors are part of the safety function and the output commands of the hardwired safety function are read by the central processing unit of the programmable controller. The module can perform its safety functions despite the presence of faults in the input/output read system or malfunction of the programmable controller, including loss of power.
The module of the invention is characterized by the fact that it comprises a safety unit composed of hardwired components that receive the plus charge of a DC power supply via a series of contacts and the zero volt charge via a series of contacts. These components also control safety relays connected to outputs to which are connected electrical apparatuses disposed on the power lines and means for reading the status of the various contacts and the status of the outputs associated with the relays.
According to one characteristic, the module comprises read units composed of discrete components that are wired in parallel to the input contacts and designed for programmable controller diagnostics.
According to another characteristic, the module comprises a read unit that reads the command status of the safety relays.